Travis: Update clang-format to 6.0

.travis.yml

@@ -6,8 +6,11 @@ matrix:
       dist: trusty
       addons:
         apt:
+          sources:
+            - sourceline: 'deb http://apt.llvm.org/trusty/ llvm-toolchain-trusty-6.0 main'
+              key_url: 'https://apt.llvm.org/llvm-snapshot.gpg.key'
           packages:
-            - clang-format-3.9
+            - clang-format-6.0
       script: "./.travis/clang-format/script.sh"
     - os: linux
       env: NAME="linux build"

.travis/clang-format/script.sh

@@ -7,7 +7,7 @@ if grep -nr '\s$' src *.yml *.txt *.md Doxyfile .gitignore .gitmodules .travis*
 fi
 
 # Default clang-format points to default 3.5 version one
-CLANG_FORMAT=clang-format-3.9
+CLANG_FORMAT=clang-format-6.0
 $CLANG_FORMAT --version
 
 if [ "$TRAVIS_EVENT_TYPE" = "pull_request" ]; then